You'll also need to tweak the source load resistor as well. George mentioned that this was one of the changes he would like to make to this PCB: allow for separate supply rails for the FETs so that they don't have to stretch all the way from B+ to B-. You wouldn't even need a B- on the PCB anymore if you supplied your own +/- 100V rails.
Obviously you can do with with a bit of trace cutting.
Obviously you can do with with a bit of trace cutting.
an update......
The amp is up and running. I'm running it on my main system with a variac at about 90% of full throttle until the Edcor XPW131 shows up.
I've been chasing a problem of one channel not working since yesterday....long story short, the vintage 4 pin ceramic socket wasn't making good contact with the tube pins, so I unsoldered the socket, extracted the contacts, re-tensioned them, and re-installed. Problem solved, at least until the contact tension Peters out again.
I ended up removing R5, R6, C6, C7 from the board and putting them on a perf board daughter board mounted to the side of the chassis. This solved two problems; the caps on the board were too tall for my chassis (they touched the bottom cover), and this change allowed me to use big honkin' Panasonic TS-ED and TS-HB snap ins. I also changed R5 to 3K 6 watt and C7 to a 180uf Panasonic TS-HB snap in. With the Hammond 273BX (350-0-350) the B- is around 230V.
I'm still trying to get the hang of this MOSFET thing; I'm assuming that the total voltage across the MOSFET (B+ to B-) needs to be at least as much as the driver tube voltage swing plus some margin, is this correct?
A few tweaks remain. The square waves are quite square, with a little wiggle/underdamped response at the top of the wave. I'm going to swap the metal films in the amp for CC, and/or use a higher value R.
The amp is up and running. I'm running it on my main system with a variac at about 90% of full throttle until the Edcor XPW131 shows up.
I've been chasing a problem of one channel not working since yesterday....long story short, the vintage 4 pin ceramic socket wasn't making good contact with the tube pins, so I unsoldered the socket, extracted the contacts, re-tensioned them, and re-installed. Problem solved, at least until the contact tension Peters out again.
I ended up removing R5, R6, C6, C7 from the board and putting them on a perf board daughter board mounted to the side of the chassis. This solved two problems; the caps on the board were too tall for my chassis (they touched the bottom cover), and this change allowed me to use big honkin' Panasonic TS-ED and TS-HB snap ins. I also changed R5 to 3K 6 watt and C7 to a 180uf Panasonic TS-HB snap in. With the Hammond 273BX (350-0-350) the B- is around 230V.
I'm still trying to get the hang of this MOSFET thing; I'm assuming that the total voltage across the MOSFET (B+ to B-) needs to be at least as much as the driver tube voltage swing plus some margin, is this correct?
A few tweaks remain. The square waves are quite square, with a little wiggle/underdamped response at the top of the wave. I'm going to swap the metal films in the amp for CC, and/or use a higher value R.
I use Alps 100K Ohm.
An externally hosted image should be here but it was not working when we last tested it.
I purchased an Alps 100k Ohm which looks just like the one in the pic (blue velvet), but it does not fit to the Tubelab SE board. I must have checked the spacing between the pins before ordering, and I can use the pot for my Aikido project anyway so nothing hurts.
Anyways, which pot fits to the board without modification?
Doug
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